#include <stdio.h>

struct Chain
{
    int data1;
    int data2;
    struct Chain *next;
};
void chain()
{
    struct Chain cdata;
    struct Chain cdata1;
    cdata.data1 = 10;
    cdata.data2 = 20;
    cdata.next = &cdata1;
    cdata1.data1 = 100;
    cdata1.data2 = 200;
    cdata1.next = NULL;
    printf("%d\n", cdata.next->data1);
}

void scan_num()
{
    int number;
    int sum = 0;
    int count = 0;

    scanf("%d", &number);
    while (number != -1)
    {
        sum += number;
        count++;
        scanf("%d", &number);
    }

    printf("%f\n", 1.0 * sum / count);
}
int main()
{
    chain();
    scan_num();
    return 0;
}